C++ How to add numbers in an array within a given range? - c++

Question

I'm working on an assignment for class and am having a bit of a hard time putting it together. I had just started learning arrays and am not sure exactly how to get user input in the array.
Here is the assignment prompt: Create a program that inputs up to 100 integers (space separated!) and outputs their sum. For example:
1 2 3 4 5 6 7 8 9 10
55
This is what I have so far (edit because I forgot to change comments):
#include <iostream>
using namespace std;
int addNum(int n);
int main() {
int n;
// prompt user to input numbers
cout << "Please enter in values to add together: ";
cin >> n;
cout << addNum(n);
// pause and exit
getchar();
getchar();
return 0;
}
// function
int addNum(int n) {
int arr[99] = {};
int sum = 0;
for (int i = 0; i < n; i++) {
sum = sum + arr[i];
}
return sum;
}

Answer 1

Since this is a learning exercise, I wouldn't correct your code, but explain what you've missed so far:
The assignment asks to read integers until there's no more input; your code prompts the user for the count upfront, which should be removed.
You do not need an array to store the individual numbers, because the assignment asks only for the total. This can be computed on the fly: read a number, add it to sum, and forget the number.
You can read numbers until the end of input with a simple loop that uses >> operator below.
Here is an example that limits the input to 100 numbers, or stops when the input stream ends:
int limit = 0;
int nextNumber;
while ((limit++ != 100) && (cin >> nextNumber)) {
... // Process the next number
}
If you are giving your program input from console (as opposed to feeding it a file with numbers) and you need to end your input sequence, press Ctrl+z on Windows or Ctrl+d on UNIX.

Answer 2

In order to provide a diverse range of answers, std::accumulate is pretty cool.
http://en.cppreference.com/w/cpp/algorithm/accumulate
int sum = std::accumulate(v.begin(), v.end(), 0);
or in your case
int sum = std::accumulate(arr, arr + 99, 0);
Another functional approach is to use std::reduce introduced in C++17
http://en.cppreference.com/w/cpp/algorithm/reduce

Answer 3

Was able to get a working code after talking to the professor about it! Here's the working code:
#include <iostream>
using namespace std;
int main() {
// variable declarations
int sum = 0, count = 0;
int c;
// array declaration
int arr[100] = { 0 };
// prompt user to input numbers & add
cout << "Please enter in values to add together: ";
for (int i = 0; i < 100; i++) {
cin >> arr[i];
c = cin.peek();
sum = sum + arr[i];
// if user presses enter, skip to outputting sum without waiting for 100 values
if (c == '\n'){
break;
}
}
// output the sum of input
cout << sum;
// pause and exit
getchar();
getchar();
return 0;
}